The projectile won't start decelerating until atmospheric pressure and friction overcomes the pressure behind the round. In this case, the air chamber is actually quite a bit bigger than it needs to be for the barrel size;

Volume of gas in chamber at 40 psi fill pressure: 12 700 ciPressure of entire system when projectile is at muzzle: 38.1 psia, quite a bit more than the 14.7 psia that the atmosphere is pushing back with, meaning that the round is still acclerating unless the friction is absurdly high.

I know that I'm aiding in kicking up a dead topic, but the SWAT gun never dies

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Spudfiles' resident expert on all things that sail through the air at improbable speeds, trailing an incandescent wake of ionized air, dissociated polymers and metal oxides.

I havent quit, I've just.... slowed down. the swat needs about $150 iin parts to become operational again, and at this point i would rather put it into a dirtbike or quad.

while I enjoy blowing things up/shooting things, I think i enjoyed the construcion of the guns just as much, if not more. I enjoy the raw mechanical aspect most!

internal combustion engines are amazng. improving power and efficency, and adapting them to various applications has proved to be a blast! just what the doctor asked for...

I buy old motorcycles and quads for a song and a dance, fix the crap out of them, and kick my friend's $2500 powersports vehicles asses, that are 15-20 years newer, with a $700 dollar piece of machinery I built myself.

it's very gratifying and amazingly fun!

my current bike goes about 80 mph, and I bought it off craigslist for $200it was in several tupperware tubs. I put it together, custom welded the exaust pipe, since I fit a engine twice as big as the one the bike orriginally came with into the frame. then I fixed/built/installed anything the bike was missing, but new tires and handlebars on it, and I am still improving! I eagerly await the muddy spring!

here's some pictures of it, although since this time I've added a plethora of parts to this bike.

While I enjoy blowing things up/shooting things, I think i enjoyed the construction of the guns just as much, if not more.

In some ways, I agree. It's great to see the results, but the building is just as much fun.

Unfortunately, the building of them is also quite a lot more expensive... (Read: Hundreds of £, $ or € for a really meaty cannon, where as a shooting session is, usually at least, some cheap ammo and targets - many of which can be things destined for the rubbish bin.)